This invention relates to an improved catalyst component and a catalyst system for use in the polymerization of .alpha.-olefins and a method of using the same, and more particularly, this invention pertains to a catalyst component for use in the polymerization of .alpha.-olefins, wherein the improved catalyst component is obtained by adding a desired quantity of an organo aluminum compound to a supported titanium (IV) halide for the polymerization of .alpha.-olefins, subjecting the mixture to a mechanical grinding treatment in the presence of a desired quantity of an ethylenically unsaturated hydrocarbon and in a preferred embodiment, subjecting further to removal of the hydrocarbon and to a mechanical grinding treatment. The invention further pertains to a catalyst system comprising the improved catalyst component and an organoaluminum cocatalyst, and a process for the polymerization of .alpha.-olefins using the catalyst system comprising the improved catalyst component, whereby the particle property, stereoregularity of the polymer are improved and catalyst activity during polymerization is improved.
Of late, various efforts have been made in the stereoregular polymerization of .alpha.-olefins using a catalyst system comprising a supported titanium halide catalyst component and an organo aluminum catalyst component.
For the preparation of a supported titanium catalyst component in such a case, there has been proposed a method comprising ball milling anhydrous magnesium chloride, an organic acid ester and silicon chloride and contacting the resulting support with liquid titanium tetrachloride with heating to thus support the titanium component (Japanese Patent Application (OPI) No. 16,986/1973). The inventors have also proposed a method comprising ball milling anhydrous magnesium chloride, an organic acid ester and titanium tetrachloride and treating the co-ground product with a hydrocarbon solution of hexachloroethane (Japanese Patent Application No. 42,147/1978), a method comprising ball milling anhydrous magnesium chloride, an organic acid ester, titanium tetrachloride and hexachloroethane (Japanese Patent Application No. 42,148/1978) and a method comprising subjecting the co-ground product to an activation treatment with a hydrocarbon solution of hexachloroethane (Japanese Patent Application No. 42,149/1978).
However, these methods having a grinding step yield catalysts having a wide particle size distribution. When .alpha.-olefins are polymerized using a catalyst having a wide particle size distribution, the resulting polymers also manifest a wide particle size distribution and the finely powdered polymers cause clogging of a filter cloth. This is an undesirable result in the practice on a commercial scale.
In order to prevent formation of a fine powder polymer, it is possible to employ a method comprising sieving a ground catalyst product and using the obtained catalyst having a desired particle size distribution. This method, however, results in a lowered yield of titanium catalyst and high cost.
For the purpose of preparing a titanium catalyst component with a narrow particle size distribution, there has also been proposed a method comprising preparing magnesium chloride support with a relatively uniform particle size and immersing the magnesium chloride in titanium tetrachloride, followed by heating (Japanese Patent Application (OPI) Nos. 65,999/1974 and 38,590/1977). In accordance with this method, a special step for the preparation of the support is required and there is only obtained a product having a low stereoregularity.
Japanese Patent Application (OPI) Nos. 3,068/1978 and 30,493/1978 describes a so-called double stage process, i.e., comprising an initial polymerization at a low temperature and a real polymerization, whereby the polymerization activity, stereoregularity and bulk density are improved, but this process is carried out by solution polymerization, not by polymerization in a liquid monomer.
In the prior art technique as set forth above, it is impossible to obtain a supported titanium (IV) catalyst component having a satisfactorily high activity, excellent durability of activity during polymerization, high stereoregularity and which is capable of suppressing formation of a fine powder polymer in bulk polymerization, and when using this catalyst component, the polymer yield per titanium although is sufficiently high, the polymer yield per weight of the catalyst (including the support) is not sufficient so as to be able to eliminate the ash removal step.